I believe your discernment is incorrect. For a discernment to be true, among many things, it cannot contradict what God already reveals in scripture and in tradition. Both scripture and the Church clearly teaches that God will not refuse anyone who repents. The only unforgivable sin is when we refuse to trust in His mercy.
So, your belief that you have a sin that God will not forgive, that the door to God is locked for you, that message cannot be from God, but is from the enemy. Yes, Satan knows all our details too and can use them to confuse us, to make us believe him to be from God. You must renounce this false message, and go to confession and seek help with the priest.
Remember, you are God’s child, loved beyond your wildest dream. You are the image of God, vested with glory and destined for eternal life. No sin can change this identity of yours. You need to run to God today and every day, for He has been waiting for you, longing for you all this time. Let go of this lie and entrust yourself completely in His mercy, for His mercy is greater than anything you could have done or are ever capable of doing. Yes, our sins disfigure us, but God is not turned away. In fact, like any good parents, He longs for us even more and can’t wait to embrace us and heal us, to walk with us again so that we may be converted and be set free. So, for the love of God, run to Him right away and let nothing——not your sin, not your shame, not this false message —— stop you.
Jesus, I trust in you, for your unfathomable mercy cannot fail.